Plating method, plating liquid and plated engine component

Abstract: The present invention relates to a plating method, plating liquid and plated component of an engine, in particular internal combustion engine, wherein high speed plating is performed by means of using a nickel plating liquid containing phosphorus and a dispersed eutectoid substance wherein sodium is additionally incorporated into said liquid.

Description: This invention relates to a plating method for the high speed nickel plating a liquid and a eutectoid substance, and to an engine component, in particular cylinder, having an interior surface on which a plated layer is formed with the use of the plating liquid. Hitherto a technique has been generally known in which a surface of a work is plated by impressing an electric voltage between an electrode and the work while allowing a plating liquid to be present between the electrode and the work. (DE 39 37 763 C2, FR 2 685 924 A1) various high speed plating methods have been also envisaged for enhancing the deposition speed of the plating. There is a kind of plated coating which contains a dispersed eutectoid substance. In particular, a Ni-P-SiC plated coating which contains nickel and phosphorus and in which silicon carbide eutectoid is dispersed is effective as a plating on, for example, an interior peripheral surface of a cylinder of a cylinder block of an engine formed of an aluminum cast alloy. Namely, it has thus far been known to form a cylinder wall by plating, rather than by providing a cylinder liner, an inside peripheral surface of a cylinder of a cylinder block formed of an aluminum cast alloy (see, for example, Japanese Patent Publication No. 1-52480). In this case, while chrome plating has been predominantly adopted, the above-mentioned Ni-P-SiC plating, among other things, gives excellent characteristics such as in lubricity and coefficient of friction as described hereinafter. In such plating, too, there is a demand for increasing the speed of the plating deposition. By a mere technique such as by increasing the electric current density while allowing the plating liquid containing phosphorus and a eutectoid-forming substance to flow, however, it is difficult to attain a high quality, dispersed eutectoid-containing plating which can satisfy the demand, because the formation of dispersed eutectoid substance is not accelerated so that the amount of the eutectoid substance and the content of phosphorus in the deposition layer are decreased, though the deposition speed of nickel is increased. Thus, the conventional plating with the formation of dispersed eutectoid is unavoidably performed with a low deposition speed. With the foregoing circumstances in view, it is an objective of the present invention to provide a plating method which permits the formation of a desired, high quality nickel plating containing phosphorus and a dispersed eutectoid substance at a high speed. Moreover, it is an objective of the present invention to provide an improved plating liquid to be used in the aforementioned process which allows the formation of high quality wear resistant plated surfaces under high speed plating conditions. Finally, it is an objective of the present invention to provide an engine component having improved durability by means of plated surfaces generated in a high speed plating procedure, specifically useable for plating the interior surfaces of engine cylinders. According to the present invention the above mentioned objective regarding the plating method is performed by a plating method for workpieces, such as engine components, using a nickel plating liquid containaing a dispersed eutectoid substance, phosphorus and sodium for forming a nickel plating layer on a surface of the workpiece wherein a high speed plating treatment is performed at a high electric current density while forcibly driving the plating liquid at a flow rate of 1.0 to 3.0 m/sec. to flow between the surface of the workpiece to be plated and an electrode. Preferred embodiments of said plating method are laid down in the further subclaims. According to the present invention, the above mentioned objective in terms of the plating liquid is performed in that a plating liquid is provided for plating a workpiece, in particular for forming a nickel plating layer containing a dispered eutectoid substance and phosphorus, comprising a nickel plating liquid containing sodium and phosphorus in addition to a dispersed eutectoid substance-forming material, said phosphorus concentration is 0.1 to 0.3 g/l plating bath and said sodium concentration is 1.0 to 3.5 g/l plating bath or more. Preferred embodimients of said plating liquid are laid down in the dependent claims. Finally, the above mentioned objective in terms of the engine component, in particular cylinder block, according to the present invention, is performed in that engine component, in particular engine cylinder, having a plated surface, in particular interior surface, obtainable by forming said plated surface by high speed plating treatment utilizing a plating liquid forcibly driven at a flow rate of 1.0 to 3.0 m/sec and simultaneously applying an electric current density of 20 to 200 A/dm 2 , said plating liquid comprising a nickel plating liquid containing sodium with a concentration of 1.0 to 3.5 g/l plating bath or more and phosphorus with a concentration of 0.1 to 0.3 g/l plating bath in addition to a dispersed eutectoid substance forming material wherein the plating layer contains 0.5 to 0.98% by weight of phosphorus and is produced with a plating deposition speed of the dispersed eutectoid substance-forming material of 20 to 30 µm/min. The present invention is based on the findings that when the concentration of sodium which is added to a plating bath increases, the amount of silicon carbide eutectoid as well as the phosphorus content will increase. This development is utilised for increasing the speed of the plating process and for improving the properties of the plating. With the plating liquid of the present invention there is obtainable a function wherein the content of phosphorus in the deposit layers increased by the addition of sodium therein in forming as nickel plating containing phosphorus and dispersed eutectoid substance. When silicon carbide is used as the eutectoid sustance - forming material, a function can be obtained that the amount of silicon carbide eutectoid is increased. Accordingly, when the plating liquid is used for a high speed plating process, a decrease in phosphorus content and an amount of eutectoid substance can be prevented. Especially by using the plating bath, the phosphorus concentration and the sodium concentration as indicated in the preferred embodiments of the present invention, preferred phosphorus content is obtained particularly suitable for high speed plating. According to the preferred embodiments of the present invention, the plating liquid can be effectively utilised in the plating method for high speed plating. In particular, by means of adjusting the plating liquid flow rate of 1.0 to 3.0 meter per second with an electric current density of 20 to 200 A/dm 2 the plating treatment speed can be accelerated while forming a high quality plated coating. An engine cylinder having a plated interior surface according to the characteristics of the plating method and plated coating according to the present invention, meets the requirement of nowadays interior pheripheral surfaces of cylinders for engines having high power output and long durability. In the following the present invention is explained in greater detail by means of several embodiments thereof in conjunction with the accompanying drawings wherein: Fig. 1 is a vertical, cross-sectional, front view showing an embodiment of a plating device for carrying out the method of the present invention. Fig. 2 is a vertical, cross-sectional, side view of a plating treatment section of the device. Fig. 3 is a view showing a piping system for high speed plating in the plating treatment section. Fig. 4 (a) and (b) are enlarged, cross-sectional views showing a Ni-P-SiC plated coating formed on an inside peripheral surface of a cylinder before abrasion and after abrasion, respectively. Fig. 5 is a graph showing a relationship between the temperature and the hardness of the plating. Fig. 6 is a graph showing a relationship between the load and the coefficient of friction. Fig. 7 is a graph showing a relationship between the phosphorus content and the hardness. Fig. 8 is a graph showing a relationship between the Na concentration of the plating liquid and the amount of SiC eutectoid in the plating. Fig. 9 is a graph showing a relationship between the Na concentration of the plating liquid and the phosphorus content of the plated coating. Fig. 10 is a graph showing a relationship between the phosphorus concentration of the plating liquid and the phosphorus content of the plated film. Fig. 11 is a graph showing a relationship between the phosphorus concentration of the plating liquid and roughness of the plated surface. Fig. 12 is a graph showing a relationship between the sodium concentration of the plating liquid and the roughness of the plated surface. Fig. 13 is a graph showing a relationship between the sodium concentration of the plating liquid and the hardness of the plating after a heat treatment. Fig. 14 is an explanatory view showing the condition of the plating when the phosphorus content in the plated coating is high. An embodiment of a high speed plating device used for carrying out the method of the present invention will be first described with reference to Figs. 1-3. Figs. 1 and 2 illustrate the structure of a plating treatment section in which a cylinder block 1 of a four-cylinder engine of an automobile is used as a work and in which the inside peripheral surface of each of the cylinders 2 of the cylinder block 1 is plated. In these Figures, a supporting block 12 is provided on a base table 11 of a treatment device main body 10. The cylinder block 1 which has a unitary structure composed of a part having four juxtaposed cylinders 2 and a skirt-like crank case part 3 is supported on the supporting block 12 together with a jig 40 connected to an upper end of the crank case part 3 in an inverted state as seen from the state where the cylinder block is mounted on an automobile. The supporting block 12 has a laterally (in the direction along which the cylinders are arranged) extending, treating liquid feeding path 13 and has an upper surface provided with an opening 13a, which is in fluid communication with the treating liquid feeding path 13, at a position corresponding to each of the cylinders 2 of the cylinder block 1. Thus, in the state where the cylinder block 1 is supported on the supporting block 12, the lower side opened portion (head-side opened portion) of each of the cylinders 2 of the cylinder block 1 coincides with the corresponding opening 13a with their peripheral edges being maintained in close contact with each other. The treatment device main body 10 is provided with an electrode 14 which also serves to function as a fluid passage constituting member at a position corresponding to each of the cylinders 2 of the cylinder block 1. Each of the electrodes 14 is formed into a cylindrical shape and is mounted on a holder 15, which in turn is mounted on the base table 11, through a mounting member 16. Each electrode 14 extends through the treating liquid feeding path 13 and protrudes upward from the corresponding opening 13a. In the state where the cylinder block 1 is supported on the supporting block 12 as described above, each of the electrodes 14 is inserted into the corresponding cylinder 2 of the cylinder block 1 so that the upper end of the electrode 14 is positioned adjacent to an upper end of a cylinder bore with a determined space being defined between the outer peripheral surface of the electrode 14 and the inside peripheral surface of the cylinder. As a consequence, fluid passages 17 and 18 are defined inside and outside of the electrode 14 in each of the cylinders 2 of the cylinder block 1 and are in fluid communication with each other at upper ends thereof. The outer passage 17 is in fluid communication with the treating liquid feeding path 13. Each of the holders 15 is provided with a through hole which constitutes, together with the inside space of the mounting member, a treating liquid discharging path 19 which is in fluid communication with the inner passage 18 formed in the electrode 14. The treating liquid discharging path 19 is connected to each of the treating liquid recovering pipe 34, which will be described hereinafter, through a connecting pipe 34a. The mounting member 16, holder 15 and connecting pipe 34a are formed of an electrically conductive material and are electrically connected to a rectifier (not shown). The jig 40 connected to the cylinder block 1 is provided with a plate 21 engageable with the upper end of the cylinder block 1. Further, at a position corresponding to each of the cylinders 2 of the cylinder block 1, the jig is provided with a covering member 22 for covering the upper opened portion of each of the cylinders 2. The covering member 22 is formed of a rubber or the like material into a desired curved shape and is mounted on the plate 21 through a bracket 23. And, just above the upper opened portion of each of the cylinders 2, the peripheral edge of the covering member 22 is in close contact with the inside wall surface of the crankcase portion 3 and a wall surface of a crankshaft supporting wall between the cylinders 2. Connected to each covering member 22 is a shower nozzle 24 for injecting cleaning water into the corresponding cylinder. Further, the jig 20 is provided with a liquid level sensor 25 extending into the cover 22 and serving as a safety device for preventing overflow of the plating liquid. Fig. 3 depicts a piping system for the above plating treatment section. In this Figure, a treating liquid feeding pipe 33 and a treating liquid recovering pipe 34 are provided between the treatment device main body 10 and a tank 31 containing a plating liquid and a pump 32 connected to the tank. The treating liquid feeding pipe 33 has an upstream end connected to the pump 32, and its downstream end connected to the treating liquid feeding path 13 (see figure 3) of the treatment device main body 10. The treating liquid recovering pipe 34 is connected at its upstream end to the treating liquid discharge path 19 (see figures 1 and 2 and page 8, first paragraph) of the treatment device main body 10, and its downstream side extends to the tank 31 (see figures 1 and 2 and page 8, fourth paragraph). The treating liquid feeding pipe 33 is provided with an automatic valve 35 and a manual valve 36 for adjusting the feed rate of the treating liquid and with a flow rate sensor 37 for detecting the feed rate of the treating liquid. The treating liquid recovering pipe 34, on the othe hand, is provided with an ejector 38 for forcibly sucking and recovering the treating liquid from the treatment device main body 10. In addition to the above treating liquid recirculating system, there is provided a cleaning water feeding pipe 39 for feeding cleaning water to the cylinder block 1. The cleaning water feeding pipe 39 has a downstream end connected to the shower nozzles 24 (see Figs. 1 and 2) of the jig 20 and an upstream end connected to a cleaning water supply source (not shown). In a midway of the cleaning water feeding pipe 27, an automatic valve 40 is provided for adjusting the flow rate of the cleaning water. The cleaning water after washing is allowed to flow into the tank 31 through a pipe. In order to evaporate water in an amount corresponding to the cleaning water fed to the tank, a concentrating device is provided in the tank 31. With the above plating device, the plating treatment is carried out in the following manner. In the state where the cylinder block 1 and the jig 20 are connected to each other with the upper opened portion of each of the cylinders 2 being covered with the covering member 22, the above assembly is set on the supporting block 12 of the treatment device main body 10. The plating liquid is supplied and recirculated through the piping system shown in Fig. 3 and an electrical energy is supplied to the electrode 14 shown in Figs. 1 and 2. By this, high speed plating of the inside surface of each of the cylinders 2 of the cylinder block 1 is performed. Namely, the plating liquid introduced from the treating liquid feeding pipe 33 into the treating liquid feeding path 13 of the supporting block 12 is passed, as shown by the arrow in Fig. 2, through the fluid passage 17 between the outer peripheral surface of the electrode 14 and the inside peripheral surface of the cylinder and flows through the upper space of the cylinder 2 into the fluid passage 18 formed inside of the electrode 14. The plating liquid is then forcibly sucked through the treating liquid discharging path 19 to the treating liquid recovering pipe 34 and is returned to the tank 31. The treating liquid is recirculated in the above manner. During the movement of the plating liquid along the inside peripheral surface of the cylinder which is to be plated while impressing the voltage between the electrode 14 and the inside surface of the cylinder, a high speed plating is performed. In this case, since the plating liquid which has been fed to the upper space of the cylinder 2 through the passage 17 leading from the treating liquid feeding path 13 is forcibly sucked into the passage 18 leading to the treating liquid discharging path 19 by the suction force of the ejector 38, the plating liquid is surely prevented from overflowing from the upper opened portion of each cylinder 2. Further, the covering member 22 covering the upper opened portion of each cylinder 2 serves to prevent the scattering of the plating liquid. In the manner as described above, the high speed plating treatment is suitably performed. After the plating treatment, water-washing is conducted. With the device shown in the drawings, the water-washing operation can be carried out in the same position following the plating treatment. Namely, after the plating operation has been completed, the pump 32 and the ejector 38 are stopped and, thereafter, the cleaning water is fed from the cleaning water supply source (not shown) through the cleaning water feeding pipe 39 and is sprayed into each cylinder from the shower nozzle 24 mounted on the corresponding covering member 22. The present invention provides a high speed nickel plating containing phosphorus and an eutectoid substance, e.g. a high speed plating of nickel (Ni)-phosphorus (P)-silicon carbide (SiC). This dispersed Ni-P-SiC plating has the following characteristics. When an inside peripheral surface of the cylinder of the cylinder block 1 formed of an aluminum cast alloy is plated by the Ni-P-SiC plating, there is formed a plated coating 50 composed of an Ni-P matrix 51 and eutectoid particles 52 on the inside peripheral surface of the cylinder, as shown in Fig. 4. On the surface of the plated coating 50, oil pockets 53 (Fig. 4(a)) are formed by honing for lubrication. Upon repeated reciprocation of a piston 55 during use, new oil pockets 54 are formed as a result of the abrasion of the Ni-P matrix 51 and the retention of the hard SiC eutectoid particles 52. Accordingly, the lubrication with an oil can be effected in a suitable manner for a long period of time. Upon investigation of the relationship between the temperature and the plating hardness in the above dispersed Ni-P-SiC plating, a dispersed Ni-SiC plating and a hard chrome plating, there are obtained the results shown in Fig. 5. The Ni-P-SiC plating when heat-treated at about 350 °C gives a higher hardness than that of the hard chrome plating and shows much higher hardness than that of the Ni-SiC plating containing no phosphorus. Thus, it will be appreciated that the hardness after a heat treatment can be improved by incorporation of phosphorus. Upon investigation of the relationship between the load and the coefficient of friction in the dispersed Ni-P-SiC plating, an Ni-P plating and a chrome plating, there are obtained the results shown in Fig. 6. The coefficient of friction of the Ni-P-SiC dispersion plating is smaller than that of the hard chrome plating or the Ni-P plating and, hence, can decrease the frictional resistance in the sliding surface. In order to utilize such merits of the dispersed Ni-P-SiC plating, it is necessary that the amount of the SiC eutectoid should be 1.5-3.5 % by weight and the hardness should be Hv600 or more (Hv800 or more after heat treatment) as the functionally suitable quality thereof. The relationship between the plating hardness and the content of phosphorus in the plated coating (when the sodium concentration in the plating liquid is 2 g/l) after the plating and after the heat treatment is as illustrated in Fig. 7. As the phosphorus content increases, the hardness increases. Thus, in order to obtain a required hardness, it is necessary to increase the phosphorus content. Next, concrete examples of the plating liquid and plating method will be described. The plating liquid of the present invention is a nickel plating liquid which contains phosphorus and an eutectoid substance-forming material such as SiC and in which sodium is additionally incorporated. The plating liquid will be more particularly described below. The plating bath for the Ni-P-Si plating is a sulfamic acid bath containing nickel sulfamate as a major component or a sulfuric acid bath containing nickel sulfate as a major component. The bath additionally contains phosphorus and silicon carbide as a dispersing agent. Sodium (Na) is further added into the this bath. Sodium hydroxide has been sometimes used for the control of the pH of a plating bath. Separately, sodium is additionally added. The preferred conditions of the composition and control of the plating bath involve the use of a nickel sulfamate or nickel sulfate bath having a concentration of the main component of 500-700 g/l, a phosphorus concentration and a sodium concentration in the plating bath of 0.1-0.3 g/l and 1.0-3.5 g/l or more, respectively, a bath temperature of 65-80°C and a pH of 3.0-4.5. The reason of the preferability of the above ranges for the phosphorus and sodium concentrations in the plating liquid will be described hereinafter. As a plating method using the above plating liquid, a device, for example, as shown in Figs. 1-3, is used for carrying out a high speed plating treatment by allowing the plating liquid to flow through a surface of a work to be plated. The preferred plating treatment conditions involve a flow speed of the plating liquid relative to the surface to be plated of 1.0-3.0 m/sec and an electric current density of 20-200 A/dm 2 . Table 1 shows a comparison between the example of the present invention and a conventional method with respect to the conditions of the plating methods, the method of the treatment, the deposition speed, etc. Conventional Method Method of the Example of the Present Invention Plating Bath Sulfamic acid bath Sulfamic acid bath (sulfuric acid bath) Plating Condition pH: unknown pH: 3.0-4.3 Bath temperature: 57 ± 3°C Bath temperature: 65-80 °C Flow Speed Between Electrodes Only stirring of the liquid in the tank 1.0-3.0 m/sec Electric Current Density 20 A/dm 2 or less 20-200 A/dm 2 Treatment Method Immersion in the tank Work and Electrode: fix Plating liquid: flow Deposition Speed (SiC Deposition Amount: 2.5 wt%) 0.5-3 µ/min 20-30 µ/min Pre-Treatment Double zinc substitution method Alumite method As will be evident from the above table, the plating deposition speed at which a required amount of the SiC eutectoid is obtainable in the example of the present invention is much higher than that in the conventional method. Thus, by the method according to the present invention, a high speed Ni-P-SiC plating is accomplished. In particular, by the incorporation of sodium in the plating bath, the amount of SiC eutectoid and the phosphorus content can be increased as required while increasing the plating deposition speed. For example, in the case of a SiC eutectoid amount of 2.5 % by weight, the plating deposition speed is as high as 20-30 µ/min. In this method, the above current density is related to the flow rate of the plating liquid. Namely, the higher the flow rate of the plating liquid, the higher becomes the current density. When the flow rate of the plating liquid is 1.0 m/sec (current density of 20 A/dm 2 ) or more, the plating deposition speed can be accelerated. When the flow rate of the plating liquid exceeds 3.0 m/sec (current density of 200 A/dm 2 ), however, the amount of the SiC eutectoid tends to significantly decrease so that it is difficult to ensure a high amount of the SiC eutectoid even with the addition of sodium. Thus, the flow rate of the plating liquid and the current density are preferably in the ranges as described above. The effect of the incorporation of sodium in the plating bath will now be described based on the results of experiments shown in Figs. 8-12. The results of the experiments shown in these Figures are obtained in the plating conducted under the following conditions. (1) Plating Bath: nickel sulfamate about 500 g/l (2) Bath Temperature: about 70 °C (3) Flow Speed of Plating Liquid between Electrodes: about 2.5 m/sec (4) Electric Current Density: about 100 A/dm 2 (5) pH: 4.0 Fig. 8 shows a relationship between the concentration of Na in the plating liquid and the amount of SiC eutectoid in the plated coating (when the SiC concentration in the plating liquid is 150 g/l) and Fig. 9 shows a relationship between the concentration of Na in the plating liquid and the amount of phosphorus in the plated coating (when the phosphorus concentration in the plating liquid is 0.3 g/l). As will be appreciated from the results of the experiments, both the amount of SiC eutectoid and the amount of phosphorus in the plated coating increase with the increase of the sodium-concentration in the plating liquid. The sodium concentration in the plating liquid of 1.0 g/l or more is much higher than that attained by the addition of sodium hydroxide for the purpose of controlling the pH of the plating bath and can give the functions that the amount of the SiC eutectoid and the content of phosphorus are increased. Fig. 10 shows a relationship between the phosphorus concentration in the plating liquid and the phosphorus content in the plated coating (no sodium is added), Fig. 11 shows a relationship between the phosphorus concentration in the plating liquid and the roughness of the plated surface (no sodium is added), and Fig. 12 shows a relationship between the sodium concentration in the plating liquid and the roughness of the plated surface (phosphorus concentration in the plating liquid: 0.3 g/l). As shown in the experimental results of Fig. 10, the phosphorus content in the plated film can be increased by an increase of the concentration of phosphorus in the plating liquid. As shown in the experiment results of Fig. 11, however, the increase of the phosphorus concentration in the plating liquid causes an increase in the roughness of the plated surface. This accelerates enlargement of the plating in edge portions of the work to cause such problems that the processability of honing to be conducted after the plating is adversely affected. On the other hand, as shown in the experiment results of Fig. 12, even when the concentration of sodium in the plating liquid is high, the roughness of the plated surface is not affected. Thus, high speed plating can be performed while ensuring sufficient amount of SiC eutectoid and phosphorus content in the plated coating and maintaining good plated surface roughness by the addition of sodium while maintaining the concentration of phosphorus in the plating liquid relatively low. Fig. 13 shows the relationship between the sodium concentration in the plating liquid and the hardness after the heat treatment (350 ° C, 1 hour) in the case where the phosphorus content in the coating is 0.65 % by weight. As shown in this Figure, when the sodium concentration in the plating liquid exceeds about 3.5 g/l, the hardness of the plating after the heat treatment tends to be lowered. Therefore, it is preferred that the sodium concentration in the plating liquid be in the range of 1.0-3.5 g/l for reasons of prevention of the lowering of the hardness caused by the increase of the sodium concentration while ensuring the effect of the increasing of the amount of SiC eutectoid and the phosphorus content. As shown in Table 2 described in detail below, the hardness and surface roughness of the plated coating are good when the phosphorus content in the plating liquid is 0.1-0.3 g/l in performing high speed plating with the plating liquid having a sodium concentration in the above-described range. As seen from the foregoing data, Ni-P-SiC plating can be effectively performed at a high speed and a high quality, plated coating is obtainable when the phosphorus concentration and sodium concentration are specifically set in the ranges of 0.1-0.3 g/l and 1.0-3.5 g/l, respectively. The relationship between the quality of the plated coating and the phosphorus concentration in the plating liquid and the phosphorus content in the coating in the Ni-P-SiC plating of an interior peripheral surface of a cylinder of an engine will be described with reference to Tables 2 and 3 which show the results of tests performed by the inventors. Table 2 shows the results of tests for sectional hardness, adhesion strength, surface roughness after plating and synthetic evaluation of plating on the interior surface of the cylinder at various phosphorus concentrations in the plating liquid and the phosphorus contents in the coating. The test conditions include a sodium concentration in the plating liquid of 3 g/l . The plating was performed by a method utilized in the example of the present invention shown in Table 1. Table 3 shows the results of tests for the adhesion strength at various phosphorus contents in the plated coating. The conditions are the same as in Table 2 except that a high speed alumite method and a zinc treatment method are selected as a pretreatment method. The adhesion strength test shown in Tables 2 and 3 was carried out in accordance with the punching test (thickness of plated coating: 100 µm). Example 1 2 3 Comparative Example 1 2 3 4 Phosphorus Concentration in Plating Liquid (g/l) 0 0.1 0.2 0.3 0.4 0.5 1.0 Phosphorus Content in Plated Coating (wt %) 0 0.55 0.65 0.98 1.40 1.58 3.14 Sectional Hardness (Vickers Load: 100gr) After plating 554 620 642 675 724 724 557 poor good good good good good poor After heat treatment (350° C, 1 hr) 380 800 850 850 850 850 750 poor good good good good good poor Adhesion Strength (5 rank evaluation) 5 5 5 5 5 4 2 good good good good good fair poor Surface Roughness after Plating (thickness: 100 µm) RZ7.5 RZ18 RZ23 RZ30 RZ50 good good good good fair Synthetic Evaluation Phosphorus Content in Coating (wt %) Pretreatment Method Adhesion Test Result (5 rank evaluation) 0 Zinc substitution method 4 fair 0.1 High speed alumite method 5 good 0.3 Zinc substitution method 4 fair 0.5 High speed alumite method 5 good 0.9 Zinc substitution method 3 poor 0.9 High speed alumite method 5 good 1.5 High speed alumite method 4 fair 4.0 Zinc substitution method 2 poor As shown in Table 2, in Example 1 in which the phosphorus concentration in the plating liquid is 0.1 g/l and the phosphorus content in the plated coating is 0.55 % by weight, in Example 2 in which the phosphorus concentration is 0.2 g/l and the phosphorus content is 0.65 % by weight, and in Example 3 in which the phosphorus concentration is 0.3 g/l and the phosphorus content is 0.98 % by weight, the sectional hardness meets with the requirement as a plated coating on the interior surface of the cylinder (Hv of 600 or more after the plating and Hv of 800 or more after the heat treatment) and, at the same time, the adhesion strength is high, the surface roughness is good and the synthetic evaluation is "acceptable". On the other hand, in Comparative Example 1 in which the phosphorus concentration and the phosphorus content are each zero, the sectional strength is insufficient so that the synthetic evaluation is "unacceptable". In Comparative Examples 2, 3 and 4 in which the phosphorus concentration is 0.4 g/l or more and the phosphorus content is 1.40 % by weight or more, the surface roughness becomes worse and the adhesion strength becomes lowered as the phosphorus content increases, so that the synthetic evaluation is "unacceptable". As shown in Table 3, the adhesion strength is better when the high speed alumite method is employed as the pretreatment method as compared with the case where the zinc substitution method is employed. In Table 3, too, it is appreciated that the adhesion becomes lowered as the phosphorus content in the coating increases. The influence of the phosphorus content in the plated coating formed by the high speed plating upon the conditions of the plated coating will be particularly described. When the phosphorus content is 1.o % by weight or more, the smoothness of the plated coating on the interior surface of the cylinder is adversely affected. Especially when a two-cycle engine cylinder having a cylinder peripheral wall provided with intake and exhaust ports is plated, a protruded portion 50a which is so called "formation of flower" is formed around the port 60 in the plated coating 50 formed on the interior surface of a cylinder 2, as shown in Fig. 14, so that the smoothness is considerably deteriorated. Moreover, the surface roughness becomes bad so that man-hours in a honing step must be increased and the service life of a grinding stone is adversely affected. Especially, since a coating having a highly accurate thickness is obtainable in the high speed plating, the man-hours in the honing step would be reduced by making the coating thickness thin. However, when the phosphorus content is 1.0 % by weight or more, the above problem is caused. when the phosphorus content is excessively small, on the other hand, the hardness will be lowered. Thus, in order to satisfy the required hardness, the phosphorus content should be 0.50 % by weight or more. Accordingly, when a nickel plating coating is formed on an interior surface of a cylinder by the high speed plating treatment, the phosphorus content is preferably in the range of 0.50-0.98 % by weight. As described in the foregoing, the plating liquid and the plating method using same according to the present invention permits high speed, phosphorus-containing nickel plating suitable for the plating of an inside peripheral surface of a cylinder, etc. In particular, using the phenomenon that the phosphorus content can be increased and the amount of the SiC eutectoid when SiC is used as a eutectoid-forming material can be also increased by incorporation of sodium in the plating bath, the high speed dispersion plating is accomplished while ensuring both sufficient phosphorus content and sufficient amount of the SiC eutectoid. Additionally, when a plated coating is formed on an interior peripheral surface of an engine cylinder by the high speed plating using the above plating liquid such that the phosphorus is contained in the plated coating in an amount of 0.50-0.98 % by weight, it is possible to obtain an engine cylinder having a high quality plated inside surface having good hardness, adhesion and surface roughness.

Claims: Plating method for workpieces, such as engine components, using a nickel plating liquid containing a dispersed eutectoid substance, phosphorus and sodium for forming a nickel plating layer on a surface of the workpiece wherein a high speed plating treatment is performed at a high electric current density while forcibly driving the plating liquid at a flow rate of 1.0 to 3.0 m/sec. to flow between the surface of the workpiece to be plated and an electrode. Plating method as claimed in claim 1, characterized in that the plating takes place while a voltage is impressed between a pair of electrodes and an electric current density of 20 to 200 A/dm 2 is adjusted. Plating method as claimed in claim 1 or 2, characterized in that the dispersed eutectoid substance is silicon carbide. Plating method as claimed in at least one of the preceding claims 1 to 3, characterized in that the nickel plating liquid comprises a nickel sulphamate bath or nickel sulphate bath. Plating method as claimed in at least one of the preceding claims 1 to 4, characterized in that the phosphorus concentration is 0.1 to 0.3 g/l plating bath. Plating method as claimed in at least one of the preceding claims 1 to 5, characterized in that the sodium concentration is 1.0 to 3.5 g/l plating bath or more. Plating method as claimed in at least one of the preceding claims 1 to 6, characterized by the following conditions: a sulphuric acid bath having a bath temperature of 65° to 80°C, a flow speed of the plating liquid of 1.0 to 3.0 m/sec., an electric current density of 20 to 200 A/dm 2 , holding the workpiece and the electrode stationary, and a deposition speed of the dispersed eutectoid substance-forming material of 20 to 30 µm/min. Plating liquid for plating a workpiece, in particular for forming a nickel plating layer containing a dispersed eutectoid substance and phosphorus, comprising a nickel plating liquid containing sodium and phosphorus in addition to a dispersed eutectoid substance-forming material characterized in that the phosphorus concentration is 0.1 to 0.3 g/l plating bath and that the sodium concentration is 1.0 to 3.5 g/l plating bath or more. Plating liquid as claimed in claim 8, characterized in that the dispersed eutectoid substance-forming material is silicon carbide. Plating liquid as claimed in claims 8 or 9, characterized in that the nickel plating liquid comprises a nickel sulphamate bath or a nickel sulphate bath. Engine component, in particular engine cylinder, having a plated surface, in particular interior surface, obtainable by forming said plated surface by high speed plating treatment utilizing a plating liquid forcibly driven at a flow rate of 1.0 to 3.0 m/sec and simultaneously applying an electric current density of 20 to 200 A/dm 2 ,said plating liquid comprising a nickel plating liquid containing sodium with a concentration of 1.0 to 3.5 g/l plating bath or more and phosphorus with a concentration of 0.1 to 0.3 g/l plating bath in addition to a dispersed eutectoid substance-forming material wherein the plating layer contains 0.5 to 0.98% by weight of phosphorus and is produced with a plating deposition speed of the dispersed eutectoid substance-forming material of 20 to 30 µm/min.

Inventors: MASAAKI ISOBE, YASUYUKI MURASE, MASAAKI, ISOBE, YASUYUKI, MURASE
Applicants: YAMAHA MOTOR CO LTD, YAMAHA HATSUDOKI KABUSHIKI KAISHA
Application year: 1994
Main classification: C25D3
IPC codes: C25D15, F02B77, F02F1, C23C18, C25D5